[zeromq-dev] Publish / Subscribe vs Multicast

gonzalo diethelm gdiethelm at dcv.cl
Mon Feb 15 21:07:43 CET 2010

> > Can I have a module with just a ZMQ_DOWNSTREAM socket, or with just
> > ZMQ_UPSTREAM socket? Or should they always be used in pairs? Sorry
> > this is a dumb question.
> It's pretty straightforward. The upmost component uses a single
> ZMQ_DOWNSTREAM socket to send messages.
> All the components in the middle of the chain use one ZMQ_UPSTREAM
> socket to get messages and one ZMQ_DOWNSTREAM socket to send them
> The last component in the chain uses single ZMQ_UPSTREAM socket to get
> the results.

Ok, got it. Some additional questions; please keep in mind this is my
first foray into ZMQ.

The original code does a lot of wiring to point the outputs of some
programs to the inputs of other programs. As one example, send_requests
creates an "exchange" called SEND_REQUESTS_OUT; later on, component1
creates a "queue" called COMPONENT1_IN and "binds" SEND_REQUESTS_OUT to
COMPONENT1_IN. Additionally, this all seems to depend on an external
process called zmq_server.

It seems in ZMQ 2.0 this binding of names and the zmq_server process are
gone, right? So all I have to do is to specify proper endpoints for each
of the current socket bind and connect calls?

One other question: I reviewed the zmq_streamer.cpp source and noticed
that both in_socket and out_socket are bound AND connected. Is this
correct? Why would that be necessary? Shouldn't in_socket only be bound,
and out_socket only be connected?

Any other hints?

Gonzalo Diethelm

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